A. Field of the Invention
This invention relates generally to the field of devices used to measure electrical biopotential signals generated by a human body, such as electrocardiogram (ECG), electroencephalogram (EEG) and electromyography (EMG) signals. More particularly, the invention relates to a wireless signal acquisition system and over the air communications protocol that is used between a plurality of wireless, remotely programmable transceivers, each coupled to a conventional patch electrode, and an associated base unit. The base unit obtains a patient's ECG, EEG or EMG signal from the wireless transceivers and supplies the signal to monitor unit for display. The wireless communications protocol allows the base unit to remotely configure and manage the wireless transceivers, prior to and during data acquisition and transmission.
B. Statement of Related Art
Conventional ECG monitoring typically requires direct wired electrical connections between electrodes that are attached to the body of the patient at one end and to an ECG monitor on the other end. Electric bio-potentials are measured at the electrodes and signals are transformed via bipolar and unipolar leads into an electrocardiogram.
Conventional ECG apparatus for hospital bedside monitoring typically requires up to ten wired electrodes. Each electrode is attached to the body of the patient, and has a wire, several feet or more in length, leading to an ECG monitor. The lengthy wired electrodes of conventional ECG apparatus obstruct the patient and limit the patient's freedom of movement. They are also cumbersome for the physician or assisting nurse.
Telemetry systems for wireless ECG monitoring for patients in hospitals currently exist. These systems are more expensive, intended for greater range (higher power), and do not totally eliminate the physical electrode wires attached to the patient. Instead of being connected to the monitor, the electrodes are each wired to a single transmitter box that is worn by the patient. Some telemetry systems also may not handle a 12 lead ECG (10 wires) because of the wiring that is required between the electrodes and the transmitter box. For example, the Spacelabs Ultraview Modular Digital Telemetry system can only handle a maximum of four leads (5 wires).
Wireless medical monitoring and diagnosis systems have been proposed in the prior art. U.S. Pat. No. 5,862,803 to Besson et al. describes a wireless electrode/sensor patch system with sensor, controller and transceiver electronics contained in an electrode patch assembly. U.S. Pat. Nos. 5,307,818, 5,168,814 and 4,981,141, all issued to Segalowitz, describe a wireless electrode system for ECG monitoring. The Besson et al. and Segalowitz patents are incorporated by reference herein. The Segalowitz patents describe a single piece electrode patch with built-in microchips for wireless one way communication, and a snap on electronic-assembly that fastens to a disposable electrode patch. However, the electrode patch is a special two-conductor type that is not conventional. The electrode assemblies are either transmit only or receive only (not both). A reference signal (generated from a Wilson network) is transmitted from the base unit to only the Right Leg electrode patch, which is receive only. Electrodes can only be programmed via manual switches on the electrode casing, not over-the-air from the base unit. For the multiple electrode embodiment, the base unit contains multiple receivers and antennas which imply multiple transmit frequencies are required for the system and over-the-air signaling (thus making the base unit more costly to implement). There is no mention of error correction or detection capability in the electrodes or base unit.
In another embodiment of the Segalowitz '818 patent, there is discussion of a single strip assembly which contains all of the electrodes required for 12-lead ECG monitoring with microchip circuitry contained in the strip assembly (not in the individual electrode patches). In this configuration, the ECG signals from each electrode are multiplexed and transmitted from a single transmitter (contained in the strip assembly) via time multiplexing on a single digitally encoded frequency channel. However, no time multiplexing on a single frequency channel is discussed for their multiple transmit electrode embodiment.
The purpose of the invention is to define a communication protocol, i.e., set of command procedures, for a wireless (leadless) electrode system that replaces the physical wires between the electrodes attached to the patent and the monitoring system base unit. The definition of communication protocols or procedures for programming the electrodes over-the air is necessary to provide flexibility in configuring the wireless electrode system to the variable environmental conditions that exist across a wide scope of patent population, as well as different application area or needs. The wireless system allows the patient a greater degree of mobility within the neighboring area without worry about accidentally disconnecting the electrodes or being disconnected from the monitoring equipment. A wireless monitoring system also provides better patient safety since the patient is electrically isolated from the monitor. This monitoring system is also more immune to noise artifacts since the digitization process of the data occurs right at the electrode measurement point and not through extended wires. The protocol defined herein describes initialization, configuration, and management of the wireless electrode network. It also describes data acquisition and transfer to the base unit that synchronizes and coordinates electrode functions.